The present invention relates to a memory device for storing information in the form of bubbles of cylindrical magnetic domain, so-called magnetic bubbles, and more particularly, to a magnetic bubble memory device using a bubble propagation path formed by ion implantation and a bubble propagation path formed of magnetically soft elements in combination.
In order to realize a magnetic bubble memory device of high packaging density, formation of the bubble propagation path by ion implantation is now under examination. In such a device, ions such as He.sup.+ are implanted in accordance with a predetermined pattern on the surface of a bubble supporting layer, in which a magnetic buble is held and propagated, so as to form a region in which magnetization is directed in the plane of the bubble supporting layer thereby to form a bubble propagation path. This propagation path (will be hereafter termed "ion-implantation propagation path") is formed in a pattern without a gap, facilitating lithographical processes, and is advantageous for fabricating a device of high packaging density. However, in order for the magnetic bubble memory to be completed, the device needs to have functional portions for generating, replicating and detecting a magnetic bubble and controlling the propagation of the bubble, in addition to storage loops formed by the propagation path. With regard to the ion-implantation propagation path, there have not been achieved a replicater for making a replica of data on a propagation path and a swap gate for controlling data exchange between two propagation paths with satisfactory operational stability.
On the other hand, with regard to the propagation path formed of an alignment of magnetically soft elements such as permalloy (will be hereafter termed "soft-magnetic element propagation path"), there have been realized replicaters and swap gates which operate stably, but it is disadvantageous for fabricating a device of high packaging density due to a certain gap width between patterns beyond which the gap can not be narrowed.
A copending U.S. patent application, Ser. No. 375,344, Sugita et al., filed on May 5, 1982 discloses a compound magnetic bubble memory device which realizes high packaging density and also stable operation. In this compound magnetic bubble memory device, the majority of storage loops (minor loops) are formed of an ion-implantation propagation path, and a read line for reading out data from the minor loops, a write line for writing data onto the minor loops, and a switch or replicater for connecting the read/write lines to the minor loops are formed of magnetically soft elements.